Optical data transceiver modules convert optical signals received via an optical fiber into electrical signals, and convert electrical signals into optical signals for transmission via an optical fiber. In the transmitter portion of a transceiver module, an opto-electronic light source such as a laser performs the electrical-to-optical signal conversion. In the receiver portion of the transceiver module, an opto-electronic light detector such as a photodiode performs the optical-to-electrical signal conversion. A transceiver module commonly also includes optical elements or optics, such as lenses, as well as electrical circuitry such as drivers and receivers. A transceiver module also includes one or more connector receptacles to which an optical fiber cable can be connected. The light source, light detector, optical elements and electrical circuitry can be mounted within a module housing. Various transceiver module configurations are known.
A transceiver module can employ wavelength division multiplexing (WDM), such as coarse wavelength division multiplexing (CWDM), to achieve more than one channel over a single fiber. WDM techniques are commonly employed in bidirectional transceiver modules. The opto-electronics of a WDM bidirectional transceiver module commonly include a laser that emits light of a first wavelength and a photodiode that receives light of a second wavelength. The optics of a WDM transceiver module commonly include one or more bandpass filters that are highly transmissive to some wavelengths and highly reflective to other wavelengths. The light beams are thus communicated along paths that include the one or more filters between the end of the fiber and the laser and photodiode. Due to space constraints and mechanical mounting considerations in the module, these elements can be positioned relative to one another in a manner that results in the optical path having a “zigzag” shape. For this reason, such a technique of implementing CWDM in a transceiver module is referred to as a “zigzag.”